JPH11168322A - Antenna device for low orbit satellite communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized and light-weight antenna device for low orbit satellite communication capable of tracking a low orbit (LEO) satellite at a high speed in a small-sized satellite earth station using the LEO satellite. SOLUTION: This antenna device 100 uses an offset paraboloidal antenna reflection mirror antenna and a primary radiator 1 is installed at the focus position of a paraboloid for forming a reflection mirror. The offset amount of an offset paraboloidal antenna is selected so as to be a value for maximizing antenna gain at a lowest operating elevation angle. Also, the primary radiator 1 is mechanically independent of the reflection mirror 2 in a movable structure and attached and fixed to a radiator supporting part 5. In the meantime, the reflection mirror 2 is rotated centering an Az axis and an EL axis by an Az-EL mount 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The antenna device for low-orbit satellite communication according to the present invention is particularly applicable to a plurality of low-orbit satellites (LEO: Low).
Earth Orbit) is used for a satellite earth station of a mobile satellite communication system orbiting the earth, and relates to a low-orbit satellite communication antenna apparatus for automatically tracking each satellite.

[0002]

2. Description of the Related Art Recently, a large number of LEO satellites have been assigned to the Ka band (30G
There is a plan to provide high-speed data of several Mbps to several tens Mbps to users all over the world using a high frequency signal of (Hz / 20 GHz).

In such a mobile satellite communication system using a large number of LEO satellites, each satellite falls out of the field of view in a relatively short time when viewed from a small earth station, so that it is necessary to track the satellite over a wide range.

Conventionally, a plurality of technologies for tracking satellites have been widely known as antennas for earth stations for geostationary satellites and mobile satellites.

For example, as a tracking method, a mono-pulse track method in which the antenna or the beam is continuously detected at the center of the beam and the direction of the satellite is constantly controlled, and the antenna is slightly moved at fixed time intervals. There are known a step track method of moving the antenna in a direction in which the reception level is maximized, and a program track method of changing the antenna direction based on satellite orbit prediction information.

[0006] As a method of supporting a movable antenna,
For example, the azimuth (Azimuth) and the elevation (Eleva)
The AZ-EL mount for moving the XY-axis and the XY-mount for moving in the direction orthogonal to the satellite orbit are widely known. The AZ-EL mount is the most widely used method at present, with one axis (Az axis) installed vertically to the ground and the other axis (El axis) installed horizontally. XY
The mount consists of an x-axis horizontal to the ground and a y-axis orthogonal to it, the y-axis rotating with the x-axis. It is suitable for tracking low-altitude satellites that move around the zenith at high speed, but it has mechanical drawbacks because both axes are located higher than the ground.

Next, a conventional concrete satellite tracking technique of an antenna of a satellite earth station will be described with reference to the drawings.

FIG. 11 is a diagram showing a configuration of a conventional antenna of a satellite earth station. This figure is an example of an antenna for a large satellite earth station. The main reflector is a Cassegrain antenna having a diameter of 13 m. And the satellite tracking of this antenna is A
A jack screw drive mechanism is used for both the Az axis and the EL axis using the drive mechanism of the z-EL mount. In order to simplify the structure, it can be continuously driven only in the range of ± 10 ° in the Az direction. If it is necessary to point the antenna in a larger direction in another direction, loosen the set screw and turn it over time. A limited drive system is adopted. With respect to the EL axis, continuous driving between 0 and 90 ° is possible. In addition, the primary radiator was attached to the main reflector and was driven integrally with the main reflector.

FIG. 12 shows an example of antenna tracking of another conventional satellite earth station, which uses an aperture antenna in the same manner as the above-mentioned large satellite earth station, but which is small and lightweight. Antenna devices are known.

FIG. 1 shows a parabolic antenna used in the Inmarsat standard A vessel earth station, in which a cross dipole and a reflector are placed as a primary radiator at the focal point of a rotating parabolic reflector. This antenna is also formed by integrating the reflector and the radiator. Then, for satellite tracking, the parabolic antenna is driven using a four-axis mount combining the above-described Az-EL mount and XY mount.

The above technology is described in "Introduction to Maritime Satellite Communications, by Toshio Sato, published on July 25, 1986, by the Institute of Electronics and Communication Engineers".

[0012]

As described above, the satellite tracking technology used in the conventional satellite communication antenna can be effectively applied to a case where the tracking range is relatively small like a geostationary satellite. It is not suitable for a low-orbit satellite communication antenna device that tracks a simple LEO satellite for the following reasons.

That is, in the conventional satellite communication antenna apparatus, the primary radiator and the reflecting mirror are integrated to rotate the antenna in the satellite tracking, so that the weight of the antenna to be rotationally driven is increased, and the driving system is also large. This makes it difficult to perform high-speed tracking and increases the area of the radome that houses the antenna. In a mobile satellite communication system using LEO satellites, the total size of the antenna device must be as small and lightweight as possible, considering that a large number of small satellite earth stations are installed in each home. Become.

Further, since the primary radiator and the reflector are integrated to rotate the antenna, it is necessary to use a low-noise amplifier or a high-frequency power amplifier in order to stably supply power to the primary radiator by rotation. It is necessary to provide a power supply system so that the RF transmitter / receiver is also mounted near the primary radiator. In this case, however, the weight of the RF transmitter / receiver increases.

In this case, it is conceivable to fix the RF transmission / reception unit separately from the reflecting mirror. There is a problem in that the antenna must be set up or a rotary joint or the like must be used, resulting in a complicated and expensive satellite communication antenna.

As described above, the object of the present invention is to use a small satellite earth station for transmitting and receiving to a large number of LEO satellites,
It is an object of the present invention to provide a small orbit low-orbit satellite communication antenna device capable of tracking a LEO satellite at high speed.

[0017]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, a low-Earth-orbit satellite communication antenna apparatus according to the present invention is used for a low-Earth-orbit satellite communication used on the ground side of a mobile satellite communication system using low-Earth orbit satellites. In the antenna device, the low-orbit satellite is mechanically tracked using an offset aperture antenna (offset antenna). Here, in the mechanical tracking, the primary radiator of the aperture antenna is fixed, and only the reflector of the aperture antenna is centered on the azimuth (Az) axis and the elevation (EL) axis in the direction of the low-orbit satellite. It is characterized by rotating and tracking.

Further, the present invention provides a low-orbit satellite communication antenna apparatus used on the ground side of a mobile satellite communication system using low-orbit satellites, wherein the reflecting mirror has a predetermined offset paraboloid of revolution. An Az-EL mount that connects to a reflector and rotates the reflector about an azimuth (Az) axis and an elevation (EL) axis to track the low-orbit satellite, and emits a predetermined beam to the reflector. The radiator includes a primary radiator, a power supply unit that supplies power to the primary radiator, and a radiator support unit that supports the primary radiator so as to be fixed independently of the reflector.

Here, the offset value is set so that the antenna gain is maximized at a predetermined minimum operation elevation angle.

Further, the predetermined minimum operation elevation angle is a tracking limit of the low-orbit satellite in the elevation direction, and is determined from the satellite altitude of the low-orbit satellite and the number of satellites arranged in the same orbit plane. And

The antenna device is an offset parabolic antenna, offset Cassegrain antenna, or offset Gregorian antenna.

The Az axis is positioned between the center of the reflecting mirror and the 1
An axis that rotates around a straight line connecting the centers of the secondary radiators 1
The EL axis is an axis that is tangent to a line that is orthogonal to the radial line passing through the rotation paraboloid of the offset reflecting mirror from the intersection (center) between the axis of the rotation paraboloid and the paraboloid. It is characterized by.

The tracking range of the low-orbit satellite is an elevation angle from the minimum operation elevation angle to the zenith, and an azimuth direction is 0 to 36.
Up to 0 °.

[0024]

Next, a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a low-orbit satellite communication antenna device of the best mode for carrying out the present invention.

Referring to FIG. 1, a low-Earth-orbit satellite communication antenna apparatus 100 of the present invention includes a primary radiator (horn) 1 for transmitting and receiving signals in the Ka band, and an offset-type reflector 2 having a predetermined paraboloid of revolution. And the Az axis and EL connected to the reflecting mirror 2
An Az-EL mount 3 that rotates the axis to track the satellite,
A feeder 4 for feeding the primary radiator 1, a radiator support 5 for fixing the primary radiator 1, an RF transmitter / receiver 6 including a low-noise amplifier and a high-frequency power amplifier, and an antenna support for fixing the entire antenna device It comprises a unit 7.

This antenna device uses an offset parabolic antenna type reflector antenna, and the primary radiator 1 is installed at the focal position of a paraboloid of revolution forming the reflector 2. The offset amount of the offset parabolic antenna is selected so as to be a value that maximizes the antenna gain at the minimum operation elevation angle described later. The primary radiator 1 has a mechanically independent structure from the reflecting mirror 2 having a movable structure, and is attached to and fixed to the radiator support 5.

On the other hand, the reflecting mirror 2 is structured to rotate about the Az axis and the EL axis by the Az-EL mount 3. The power from the primary radiator 1 is connected to the RF transmitting / receiving unit 6 via the power feeding unit 4. The Az-EL mount 3, the radiator support 5, and the RF transceiver 6 are mounted on the antenna support 7, respectively.

Next, the operation of the low-orbit satellite communication antenna apparatus 100 of FIG. 1 will be described below.

FIG. 2 is a diagram for explaining a tracking mechanism of the present antenna device, and particularly shows a reflecting mirror 2 and a primary radiator 1 related to tracking. FIG. 2A is a view of the reflecting mirror 2 and the primary radiator 1 as viewed from the front. The solid line indicates the position of the reflecting mirror 2 at the minimum operation elevation angle θMIN, and the dotted line indicates the elevation angle of about 90 °. FIG. 7 is a diagram showing the position of the reflecting mirror 2 in the case. FIG. 2B is a side view of the reflecting mirror 2 and the primary radiator 1. As is clear from this figure, the Az axis 9 is an axis that rotates around a straight line connecting the center of the reflecting mirror 2 and the center of the primary radiator 1,
Rotates 360 ° about the Az axis 9. In addition,
Reference numeral 8 denotes the axis of the paraboloid of revolution.

On the other hand, FIG. 3 is a view for explaining the EL axis. In this figure, the EL axis is the rotation of the offset reflecting mirror 2 from the intersection (center) of the axis 8 of the paraboloid of revolution and the paraboloid 9. An axis tangent to a line orthogonal to a radial straight line passing through the paraboloid in the paraboloid of revolution. It is rotated from the lowest operation elevation angle to 90 ° about this axis.

The Az-EL mount 3 drives the reflecting mirror 2 to rotate around the Az axis 9 and the EL axis 10 to perform satellite tracking.

Since the primary radiator 1 is fixed by the radiator support 5, even if the reflecting mirror 2 is movable, it is always fixed at the focal position of the paraboloid.

As described above, the satellite communication antenna apparatus of the present invention can track the omnidirectional angle in the satellite direction by rotating the reflecting mirror 2 around the Az axis. Further, by rotating the reflecting mirror 2 around the EL axis, the elevation angle of the directivity can be changed,
The directivity in the zenith direction where the elevation angle is 90 ° can be obtained.

Next, the required tracking angle range of the antenna device for low-orbit satellite communication described above will be described.

FIG. 4 is an image diagram of a LEO satellite that covers the whole world by arranging a large number of satellites on a plurality of orbit planes on the earth. As shown in this figure, a large number of LEO satellites are arranged on the earth, and any satellite can be seen at any point on the earth to provide a satellite communication system covering the whole world.

In this figure, the LEO satellite is approximately 15
It refers to a satellite in an elliptical orbit (including a circle) with an altitude of 00 km or less. If the orbital cycle of each satellite is, for example, 1000 km, it orbits the earth in about 1 hour and 45 minutes.

For example, when the altitude of a satellite is 765 km and the minimum operation elevation angle is 30 °, the number of satellites to be arranged on the same orbital plane is 20, and 1 is required to cover the whole world.
A zero orbital plane is required. That is, the total number of required satellites is 200. The required number of satellites is determined from the satellite altitude and the minimum operation elevation angle. For example, even at the same satellite altitude, the number of satellites is 98 when the operation elevation angle is 20 ° and 45 when the operation elevation angle is 10 °.

FIG. 5 is a conceptual diagram of a broadband satellite communication system provided using LEO satellites. In this figure, the system provides a small user such as a portable terminal with an L-band (1.6 GHz / 1.5 GHz) multibeam low-speed satellite link of about 64 kbps, and provides a ship, aircraft, small office Such large users are provided with high-speed data by a multi-spot beam in the Ka band (generally called a quasi-millimeter wave band and using 30 GHz / 20 GHz) at a small satellite earth station.

The present invention relates to an antenna device for low-orbit satellite communication used in small satellite earth stations mainly for the latter high-speed data users.

FIG. 6 is a diagram showing a satellite tracking range when the LEO satellite having the satellite orbit plane 11 is viewed from the small satellite earth station 13 on the ground. In this figure, as described above, L
Minimum operation elevation angle θMIN from the relationship between the number of EO satellites and altitude
Is determined, and the satellite tracking range 12 is a region indicated by oblique lines, that is, all regions in all azimuths with respect to the zenith direction from the minimum operation elevation angle θMIN.

Next, FIG. 7 is a diagram showing the relationship between the propagation loss (A) obtained by combining the free space loss with respect to the elevation angle and the loss due to rain attenuation, and the gain (B) of the offset parabolic antenna. This figure shows the sum of the propagation loss (A) and the antenna gain (B), that is, the total propagation loss (C = A + B) including the antenna gain. Here, the minimum operation elevation angle θ
MIN = 40 °. It is assumed that the offset amount is adjusted so that the antenna gain becomes maximum at the elevation angle, and the propagation loss is calculated using a transmission frequency of 30 GHz in the Ka band.

As a result, it is shown that the total propagation loss at the minimum operation elevation angle of 40 ° is the largest, and that the total propagation loss is smaller when the elevation angle is in the zenith direction.

This is because the directional gain in the zenith direction deviates from the ideal condition of the offset parabolic reflector, resulting in a decrease in the directional gain. However, in a satellite communication such as a microwave band or a millimeter wave band, the directional gain is low. In the elevation state, the satellite becomes the farthest, the free space loss increases, the distance passing through the rain area becomes the longest, and the rain attenuation becomes maximum, so that an antenna gain is required. On the other hand, these attenuations are minimized in the zenith direction.

Therefore, even if the elevation angle is set in the zenith direction by setting the minimum operation elevation angle to an appropriate value, it can be said that there is little practical problem.

The configuration using an offset parabolic antenna has been described as the first embodiment of the present invention, but the present invention is not limited to such a single reflector antenna.

That is, as the second embodiment of the present invention, an offset Cassegrain type double reflector antenna as shown in FIG. 8 can be used.

In the figure, reference numeral 12 denotes a main reflecting mirror which is a rotating parabolic reflecting mirror, and has a predetermined offset amount so as to obtain the maximum antenna gain at the minimum operation elevation angle as described above. Reference numeral 13 denotes a sub-reflection mirror formed of a rotating hyperboloid that shares the focal point of the paraboloid of revolution as one focal point. Since the primary radiator 1 has another focal point in the area of the main reflecting mirror 12, the main reflecting mirror 1
2 is provided with a circular hole 14 for beam irradiation of the primary radiator. The other reference numerals are the same as those shown in FIG.

In the present embodiment, the structure of the antenna is complicated because it is a double reflector antenna. However, since the primary radiator 1 supplies power from the back surface of the main reflector 12, reduction in power loss and transmission and reception are achieved. This has the effect of facilitating connection with the unit and preventing blocking within the tracking range.

Further, in the third embodiment of the present invention, an offset Cassegrain-type double reflector antenna as shown in FIG. 9 is used. This figure also uses the offset Cassegrain-type double reflector antenna shown in FIG. 8, but differs in that the position of the primary radiator 1 is outside the area of the main reflector 12.

Further, as a fourth embodiment of the present invention, an offset Gregorian-type double reflector antenna can be used as shown in FIG. In this figure, a predetermined amount of offset is given so that the maximum antenna gain is obtained at the lowest operation elevation angle with the paraboloid of revolution as the main reflecting mirror 15. The spheroid that shares the focal point of the paraboloid of revolution is the sub-reflector 16. At the other focal point of the spheroid, the phase center of the primary radiator 1 is located.

In the configurations described in the second to fourth embodiments using the double reflector antenna, the feed loss can be reduced as compared with the first embodiment, the primary radiator can be fixed, and the entire device can be used. Is further reduced.

[0052]

As described above, the antenna device for low earth orbit satellite communication of the present invention has the following effects.

First, since an offset parabolic antenna, an offset Cassegrain antenna, or the like that obtains the maximum gain at the lowest operation elevation angle is used, the propagation in the satellite link is achieved by optimizing the side lobe characteristics and cross polarization isolation of the antenna. The best characteristics can be obtained at the lowest elevation angle where the loss and rain attenuation are the largest. In particular, LE
This effect is particularly remarkable because the O satellite uses a millimeter wave band and thus has a large attenuation of rainfall.

Second, since the primary radiator is fixed, a flexible portion is not required for the feeder line and the waveguide, so that the structure can be simplified and the reliability can be improved.

Third, since the portion driven for tracking the satellite is only the reflector, the driving weight is small and high-speed tracking is possible, and the driving mechanism can be reduced in size and weight.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a low-orbit satellite communication antenna device (offset parabolic antenna type) according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a specific configuration of the offset parabolic antenna of FIG. 1;

FIG. 3 is a diagram illustrating a definition of an EL axis in FIG. 2;

FIG. 4 is an image diagram of a LEO satellite.

FIG. 5 is a diagram showing a mobile satellite communication system using LEO satellites.

FIG. 6 is a diagram illustrating a tracking range according to the present invention.

FIG. 7 is a diagram showing the relationship between elevation angle, propagation loss, antenna gain, and total propagation loss.

FIG. 8 is a block diagram showing a configuration of a low-orbit satellite communication antenna apparatus (offset Cassegrain type) according to a second embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a low-orbit satellite communication antenna apparatus (offset Cassegrain type) according to a third embodiment of the present invention.

FIG. 10 is a block diagram illustrating a configuration of a low-orbit satellite communication antenna device (offset Gregorian type) according to a third embodiment of the present invention.

FIG. 11 is an external view showing a conventional antenna tracking technology of a large earth station.

FIG. 12 is a conceptual diagram showing a conventional antenna tracking technology of a small earth station.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 primary radiator 2 reflector 3 Az-EL mount 4 feeder 5 radiator support 6 RF transceiver 7 antenna support 100 antenna device for low-orbit satellite communication

Claims (11)

[Claims] A low-orbit satellite communication antenna device used on the ground side of a mobile satellite communication system using low-orbit satellites, wherein an offset aperture antenna (offset antenna) is provided.
A low-Earth-orbit satellite communication antenna device, wherein the low-Earth-orbit satellite is mechanically tracked by using a satellite. 2. The machine tracking device according to claim 1, wherein a primary radiator of the aperture antenna is fixed, and only a reflector of the aperture antenna is oriented in an azimuth (Az) axis and an elevation angle (E) in the direction of the low-orbit satellite.
2. The antenna device for low-Earth-orbit satellite communication according to claim 1, wherein the tracking is performed by rotating around an L) axis. 3. A low-orbit satellite communication antenna device used on the ground side of a mobile satellite communication system using low-orbit satellites, comprising: a reflecting mirror having a predetermined offset paraboloid of revolution; Azimuth (Az) axis and elevation angle (EL)
An Az-EL mount that rotates the reflector about the axis and tracks the low-orbit satellite, a primary radiator that emits a predetermined beam to the reflector, and a power supply unit that supplies power to the primary radiator And a radiator support for supporting the primary radiator so that it can be fixed independently of the reflecting mirror. 4. The antenna apparatus for low-Earth-orbit satellite communication according to claim 1, wherein the value of the offset is set so that the antenna gain becomes maximum at a predetermined minimum operation elevation angle. 5. The predetermined minimum operation elevation angle is a tracking limit in the elevation direction of the low-orbit satellite, and is determined from the satellite altitude of the low-orbit satellite and the number of satellites arranged in the same orbit plane. The antenna device for low-orbit satellite communication according to claim 4, wherein 6. The antenna device for low earth orbit satellite communication according to claim 1, wherein said antenna device is an offset parabolic antenna. 7. The antenna device for low-Earth-orbit satellite communication according to claim 1, wherein the antenna device is an offset Cassegrain antenna. 8. The apparatus according to claim 1, wherein said antenna device is an offset Gregorian antenna.
A low-Earth-orbit satellite communication antenna device as described in the above. 9. The Az axis is an axis that rotates around a straight line connecting the center of the reflecting mirror and the center of the primary radiator 1, and the EL axis is the axis of the paraboloid of revolution and the axis of the paraboloid of revolution. The low-Earth-orbit satellite communication according to claim 2 or 3, wherein the axis is tangent to a line that is orthogonal to the radial straight line passing through the rotation paraboloid of the offset reflecting mirror from the intersection (center) in the rotation paraboloid. Antenna device. 10. The tracking range of the low-orbit satellite is an elevation direction from the lowest operation elevation angle to the zenith, and an azimuth direction is 0 to 10.
4. The antenna device for low-orbit satellite communication according to claim 1, wherein the angle is up to 360 [deg.]. 11. The antenna device for low-Earth-orbit satellite communication according to claim 1, wherein the antenna device transmits and receives a microwave band or a millimeter wave band high-frequency signal.